1. Field of the Invention
The present invention relates to a sulfur-based fertilizer and to a process for production thereof.
2. Description of the Prior Art
Sulfur and sulfur-based fertilizers are generally known. Indeed, sulfur is a very important element in the production of crops. Although it has been classified as a secondary element, many researchers are of the view that the importance of sulfur to crop growth and development parallels that of nitrogen, phosphorus and potash. As is known in the art, sulfur acts in a soil system by being oxidized to sulfate which may then be taken up by plants in the soil system.
There are many soil areas in North America where sulfur is inherently low and thus, crop production in these areas is limited. Further, the ever increasing application of other nutrients and fertilizers, together with general soil depletion, has led to increasing occurrence of sulfur-depleted soils. Generally, in order to attain efficient release of sulfur and improve plant growth in a given soil system, it is desirable to present the sulfur in conjunction with controlled amounts of other elements/nutrients such as nitrogen, phosphorus and the like. For example, in order to attain efficient release of nitrogen, phosphorus and sulfur to plants, a ratio of 10:2:1 is generally desirable. Thus, it is desirable to develop fertilizers which contain two or more elements/nutrients in a fixed amount.
Heretofore, the art has endeavoured to address the challenge of incorporating two or more elements/nutrients in a single fertilizer.
For example, U.S. Pat. No. 4,330,319 (Bexton et al.), the contents of which are hereby incorporated by reference, teaches a urea-sulfur fertilizer and a process for production thereof. Specifically, there is taught a homogeneous, solid, particulate urea sulfur fertilizer comprising a uniform dispersion of finely divided particles of sulfur in a urea matrix, the sulfur particle size being less than about 100 .mu.m. The fertilizer is produced by contacting a molten stream of urea with a molten stream of sulfur, passing the combined streams through a mixing device across which is provided a pressure drop of at least about 200 kPa to form a homogenized melt finely divided sulfur dispersed in urea and solidifying the homogenized melt to obtain the urea-sulfur fertilizer. The Examples in Bexton et al. show production of urea-sulfur fertilizers have the following grades: 43.6:0:0:6.3 and 41.6:0:0:10.5. Bexton et al. teaches a process which clearly requires contacting a molten stream of urea with a molten stream of sulfur, namely molten streams of the reactants which directly form the urea-sulfur fertilizer. Further, the fertilizer taught by Bexton et al. necessitates the presence of a significant amount of nitrogen.
It would be desirable to incorporate sulfate, for example in the form of ammonium sulfate, in a sulfur-based fertilizer since this would present to the soil system both a short term sulfur dose (i.e. in the form of sulfate) and a long term sulfur dose (i.e. in the form element sulfur which is eventually oxidized to sulfate). Unfortunately, the process described by Bexton et al. is not applicable to incorporation of a sulfate such as ammonium sulfate since, once produced, the sulfate can not be presented in a molten form.
It would also be desirable to incorporate phosphate, for example in the form of ammonium phosphate, in a sulfur-based fertilizer. The main advantage of such a fertilizer would be to combine in a single fertilizer two elements/nutrients normally required for enhanced plant growth. Again, the process described by Bexton et al. is not applicable to incorporation of a phosphate such as ammonium phosphate since, once produced, ammonium phosphate can not be presented in a molten form.
It would be desirable to have a sulfur-based fertilizer which incorporates sulphate and/or phosphate. It would be further desirable if the production of such a fertilizer could be readily incorporated into an existing production process for ammonium sulphate and/or ammonium phosphate. It would be further desirable if the production of such a fertilizer could be readily incorporated into existing solidification units (e.g. granulation drums, prilling towers and the like).